Currently, introduction of electronics to vehicles has been advanced and parts which had been mechanically controlled in the past, including engine, brake, and so forth have been replaced by electronically controlled parts. Securement of reliability is the most important factor for vehicle-mounted systems, and high reliability is required for vehicle electronic systems. The same goes for a large scale integration (LSI) circuit which is the heart of the vehicle electronic system, and it is designed so as to ensure sufficient reliability. However, problems which cannot be evaluated in an initial test may occur. Such problems include thermorunaway caused when an ambient environment has reached to a higher temperature state than supposed, degradation due to operation speed degradation and aging degradation, etc.
As means for solving such problems, there is a case where a circuit for observing status of an LSI such as temperature and operation speed is integrated within the LSI so that control is performed according to values obtained by the circuit. As control regarding temperature, an approach of lowering performance in a high temperature state to ensure reliability has been proposed. Japanese Patent Application Laid-Open Publication No. H10-200054 (Patent Document 1) describes an approach where, when a temperature of an LSI exceeds a certain fixed temperature, reliability is ensured by omitting a processing to lower an operating frequency. It is also described that an alarm lamp is lighted in that case. Japanese Patent Application Laid-Open Publication No. 2007-15413 (Patent Document 2) describes a software approach such that, when abnormality of a cooling fan is detected in a vehicle-mounted information system in which a navigation function, an audio function, an emergency notification function, an air conditioner control function, etc. are integrated, processing contents are limited so that heat generation is suppressed. It is also described that a message is conveyed to a user via display or audio to tell that the processing contents is limited.